Cristian Neagu

Fore-Arc and Back-Arc Ground Motion Prediction Model for Vrancea Intermediate Depth Seismic Source

A next generation ground motion model for the prediction of spectral accelerations both in the fore-arc and back-arc regions of the Carpathians Mountains is developed in this research for the Vrancea intermediate depth seismic source in Romania. This ground motion prediction equation (GMPE) is an updated version of the model given in Vacareanu et al. [2014] and is applicable in both the fore-arc and the back-arc regions. The strong ground motion database from which the prediction model is derived consists of over 700 triaxial accelerograms from Vrancea subcrustal seismic events, as well as from other intermediate-depth earthquakes produced in other seismically active regions in the world. The applicability of this ground motion prediction model in both the fore-arc and the back-arc region is tested using the analysis of residuals. Moreover, the appropriateness of this GMPE for soil classes B and C defined in EN 1998-1, as well as for average soil conditions is investigated. All results suggest that this model is an improvement of the previous versions of ground motion prediction equations for Vrancea intermediate-depth seismic source and its use in both the fore-arc and the back-arc regions make it a reliable candidate for more accurate seismic hazard studies of Romania.

Seismic Risk Assessment of Romania

This paper summarizes the UTCB results for the “National Risk Assessment—RO RISK” project. Within the RO-RISK project, coordinated by the General Inspectorate for Emergency Situations, the first nation-wide assessment of all types of natural risks was performed in 2016. The work was supported by collaboration of disaster reduction experts and earthquake risk modelling specialists from INFP and URBAN-INCERC. The seismic risk assessment was performed for the entire country, at the most detailed resolution available, which is the administrative-territorial unit. For each building typology, four limit states were considered in order to generate fragility curves. Each limit state is associated with a loss percentage, in order to generate vulnerability curves. The assessment shows that among the 10 analysed hazards, the seismic hazard produces the largest impact at country level, 75% of the population and 45% of the vital networks are exposed to moderate and high earthquake risk and Romania’s capital Bucharest, is highly exposed to earthquakes.

Ground Types for Seismic Design in Romania

The paper presents an overview of available data concerning ground types for seismic design in Romania. A short overview of a ground information database created during BIGSEES Romanian project is presented. A comparison of shear wave velocity for 19 sites in Bucharest determined by PS logging measurements and by Wald topographic slope method is discussed. The paper reiterates the conclusion of a study regarding the Eurocode soil factor S derived from the Romanian seismic motions. The need for an enlarged database of in situ determined ground condition is underlined, at least at the location of seismic stations. Based on borehole-specific data (geotechnical properties, hydrologic factors) and velocity profiles, evaluations of soil liquefaction potential and related indices were performed by using empirical equations proposed in literature. The application of GIS tools provided a spatial distribution of liquefaction susceptibility of Quaternary alluvial sediments in Bucharest.

Toward the Seismic Evaluation of “Carol I” Royal Mosque in Constanța

Seismic protection of cultural heritage constructions is a priority in earthquake prone countries, due to their cultural, historical and touristic importance. The paper presents a first step toward the seismic evaluation of the “Carol I” Royal Mosque in Constanța, Romania: ambient vibration measurements and the assessment of the existing damage state induced by previous earthquakes and/or other actions (index R2 according to the Romanian code for seismic evaluation of existing buildings P100-3/2008). The mosque was built in 1910–1913 and has a masonry structure with a 26 m height reinforced concrete dome. It has an approximately 40 m height RC minaret and thus it is between the first civil constructions using reinforced concrete in Romania. The construction experienced the major earthquakes of 1940 (M W = 7.7) and 1977 (M W = 7.5) and several other medium size events originating from Vrancea subcrustal seismic source without significant damage. However, the long-term climatic aggression had a negative impact on the structure. Ambient vibration measurements were performed in the minaret. The results will be used for the proper calibration of the computational model for linear analysis.

Before and After November 10th, 1940 Earthquake

The paper focuses on the evolution of seismic design of buildings in Romania with emphasis on Bucharest, “Europe’s capital of earthquakes” (The Guardian, March 25th 2014, online edition). Both seismological data available before and after the November 10th, 1940 event and data related to the damage produced by historic strong Vrancea earthquakes (1802, 1838, 1940) were presented. In the aftermath of the 1940 earthquake, new seismic design codes (1941, 1945) were introduced and macroseismic hazard maps were documented. The most representative macroseismic maps available were compared and discussed.

Prediction of Site Characterization Based on Field Investigations and Empirical Correlations

Significant damages of built environment recorded during past seismic events, closely linked to notable human and financial losses, have led to consideration of Romania’s capital city as one of the major earthquake-prone urban area worldwide. Strong historical ground shaking and extensive distribution of seismic networks have outlined that variability and specific parameters of layered unconsolidated sedimentary young deposits represents one of key component in site-response analysis. To predict seismic effects of near-surface soils, comprehensive surveys are needed for a realistic estimation of dynamic behaviour and site characterization. A large number of shallow and deep boreholes, standard penetration tests and non-invasive field techniques as down-hole and SASW measurements have been carried out in Bucharest sites. All the tests reported in the paper were performed at CNRRS (National Center for Seismic Risk Reduction) (now, Seismic Risk Assessment Research Center https://ccers.utcb.ro) and UTCB (Technical University of Civil Engineering of Bucharest). Shear wave velocities and penetration resistance have been set as main indicators in quantifying seismic properties. Empirical correlations to predict VS from N-SPT test values were developed by using statistical methods. A comparative method between soil dynamic indexes determined by in situ investigation and the ones predicted using empirical models have been performed. The end-results can be considered as guidelines to predict the potential effect of site conditions on similar soil types, layer sequences and properties.

Bi-normalized response spectra and seismic intensity in Bucharest for 1986 and 1990 Vrancea seismic events

The Vrancea subcrustal earthquakes of August 30, 1986 and May 30, 1990 are the two most recent seismic events that have occurred in Romania with moment magnitudes MW ≥ 6.9. The spectral analysis of the strong ground motions recorded in Bucharest reveals that despite small differences in magnitude between the 1986 and 1990 earthquakes, their frequency contents are very different, sometimes even opposing. The main focus of this study is to conduct a comparative analysis of the response spectra in terms of the bi-normalized response spectra (BNRS) proposed by Xu and Xie (2004 and 2007) for strong ground motions recorded in Bucharest during these two seismic events. The mean absolute acceleration and relative velocity response spectra for the two earthquakes are discussed and compared. Furthermore, the mean bi-normalized absolute acceleration and normalized relative velocity response spectra with respect to the control period TC are computed for the ground motions recorded in Bucharest in 1986 and 1990. The predominant period TP is also used in this study for the normalization of the spectral period axis. Subsequently, the methodology proposed by Martinez-Perreira and Bommer (1998) is applied in order to estimate the seismic intensity of the two events. The results are discussed and several conclusions regarding the possibility of using the bi-normalized response spectra (BNRS) are given.

Expected Direct Seismic Losses Assessment Using Gis. Case Study for Iaşi Municipality

Abstract Expected direct seismic losses assessment is performed on probabilistic basis using world-wide accepted methodologies for two study areas located in Iasi Municipality. The probabilistic assessment refers to the following issues: site-dependent seismic hazard, expected seismic response of buildings, seismic fragility of structures, expected seismic damage. The analysis of the spatial distribution of the existing building stock as well as the presentation of the results on expected direct seismic losses are performed using geographic information systems (GIS)